Metal bonded carbide compositions



Feb. 3, 1970 E G ET AL 3,493,351

METAL BONDED CARBIDE COMPOSITIONS Filed June 14, 1968 AVA $21? VVV INVENIORS HORAC In E. BERG NA ALMA U. DANIELS BY Run I ATTORNEY CARBIDE M A A Q; WW

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AVA AV AVAV METAL United States Patent 3,493,351 METAL BONDED C RBIDE COMPOSITIONS Horacio E. Bergna and Alma U. Daniels, Wilmington,

DeL, assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed June 14, 1968, Ser. No. 737,142 Int. Cl. B22f 3/12; C22c 29/00 US. Cl. 29182.7 6 Claims ABSTRACT OF THE DISCLOSURE Dense compositions having a grain size smaller than 10 microns and containing from 60 to 89 volume percent titanium, hafnium or zirconium carbide, from 10 up to 20 volume percent alumina and 1 to 20 volume percent of metal consisting of to 90 weight percent iron, cobalt or nickel and to 95 weight percent tungsten or molybdenum are useful as cutting tools for cutting steel and cast iron.

BACKGROUND OF THE INVENTION This invention relates to metal-bonded carbide cutting tools and more particularly is directed to dense compositions of titanium, zirconium or hafnium carbide; alumina; an iron group metal; and tungsten or molybdenum.

Cutting tips of carbides such as titanium carbide, and metals such as nickel and molybdenum, are well known and are presently in commercial use. (See US. Patent Reissue No. 25,815.) Such tools are effective for cutting metal but have the disadvantage of failing because of thermal cracking when operated at very high speed in turning or milling steel. This is especially true in highspeed milling of steel. There the relatively high strength of such tools would be expected to provide an advantage over brittle ceramic tools, yet they fail by chipping. The chipping apparently is the result of cracks induced by the high temperatures generated at the cutting edge and the rapid variation in temperature resulting from the interrupted nature of cutting in the milling operation as each cutting insert repeatedly enters and leaves the work material.

Alumina is very thermally shock sensitive and brittle. The problem this creates in ceramic cutting tools has not been solved by attempts to make metal-bonded aluminas or cermets. (See British Patents Nos. 841,576 and 821,596 and German Patent No. 1,072,182.) As a result, such materials are not commercially used as cutting tools.

It is surprising therefore, that the addition of minor amounts of alumina to a combination of metal carbides and metals does not exaggerate the thermal cracking effect and increase the brittleness of such compositions. On the contrary, we have discovered that within narrow ranges of composition, combinations of the four components of this invention produce cutting tips with an unusually favorable balance of properties. Thus, titanium, zirconium or hafnium carbide or their mixtures; a metal of the iron group; tungsten or molybdenum; and a minor amount of alumina, when combined within the proportional limits and with the structural characteristics set out below, produce a cutting tip which is strong, and very resistant to wear and to thermal cracking.

SUMMARY OF THE INVEN'IIION In summary, this invention is directed to dense compositions having an average grain size smaller than 10 microns and composed of 60 to 89 volume percent of zirconium, hafnium or titanium carbide or their mixtures; 1 to volume percent of metal; and from 10 up to 20 volume percent of alumina; the metal consisting of from 5 to 90 weight percent iron, cobalt, nickel or "ice their mixtures, and from 10 to weight percent tungsten, molybdenum or their mixtures.

Surprisingly these compositions demonstrate exceptional advantages over similar compositions consisting of closely related compounds and over compositions of these same compounds in different amounts. Thus the compositions of this invention offer advantages over similar compositions containing larger amounts of alumina in that the compositions of this invention are cheaper and easier to fabricate. They demonstrate increased abrasion resistance compared to metal bonded carbides and increased mechanical strength and toughness compared to ceramic tools. As a result of their exceptional properties the compositions of this invention are outstandingly useful in cutting and milling ferrous alloys at very high cutting speeds.

BRIEF DESCRIPTION OF DRAWING The figure is a graphical representation of the amounts of the components embraced within the compositional limits of this invention. The area outlined in the continuous line is that area in which the compositional ratios are within the limits of this invention.

DESCRIPTION OF THE INVENTION Components The refractory compositions of this invention consist essentially of titanium, hafnium or zirconium carbide; alumina; an iron group metal; and tungsten or molybdenum.

(a) Carbides.-The titanium, zirconium or hafnium carbide or their mixtures are used in the compositions of this invention in amounts ranging from 60 to 89 volume percent. At least 60 percent carbide must be present to insure the strength and hardness necessary for the compositions of this invention to be used in cutting steel. The maximum amount of carbide which can be present is limited to 89 volume percent because at least 10 percent of the composition must be alumina and at least 1 percent of metal is required.

The carbides suitable for use in the compositions of this invention are titanium, zirconium or hafnium carbide or their mixtures. These carbides can be obtained commercially or can be synthesized by methods Well known to the art. The carbides should have a particle size of less than 5 microns and preferably less than 2 microns. If the starting material is appreciably larger than 5 microns in particle size it can be pre-gronnd to reduce its size to that which is acceptable. Of course the milling of the components of this invention, which is carried out to obtain a high degree of homogeneity, will result in some comminution of the carbide and the other starting components.

Of the carbides, titanium carbide is preferred for use in the dense compositions of this invention as it is readily available and results in compositions which have an excellent balance of physical properties, and demonstrate great effectiveness when used to cut or mill ferrous alloys.

(b) Alumina.-The alumina is present in the compositions of this invention in amounts ranging from 10 up to but not including 20 volume percent. The need for at least 10 percent alumina is based on the desire to have the alumina present in significant amounts. Amounts of alumina below 10 percent are generally less satisfactory because the dense compositions approach too closely to the composition of the prior art metal-bonded carbides in their tendency to heat crack. Restricting the presence of alumina to up to 20 volume percent insures lack of continuity of the alumina phase under most ordinary conditions, and attendant continuity of the metal and carbide phase.

Alumina suitable for use in the compositions of this invention can be in many forms so long as it is finely divided. Thus it can be in the form of gamma, eta or alpha alumina ormixtures of these. Alpha alumina is a preferred starting material because it does not have as high a specific surface area as gamma or eta alumina and it is likely to contain less adsorbed water which can be deleterious.

The alumina to be used should be sufficiently finely divided to produce the compositions of this invention with an average grain size of less than ten microns. A suitable starting alumina is alpha alumina with a specific surface area of more than 2 m. /g. and preferably 5 to 25 mP/g. Alumina with an ultimate crystallite size of less than 0.5 micron, as measured by X-ray line broadening techniques, is particularly preferred. Such alumina can be obtained most simply by heating anhydrous aluminum diacetate to 1200 C. for 3 or more hours.

Representative of suitable commercially available alumina is Alcoa Superground Alumina XA-l6 which is characterized by X-ray examination as alpha alumina and has a specific surface area of about 13 square meters per gram which is equivalent to a spherical particle size of about 115 millimicrons.

(c) Metals-The metals employed in the compositions of this invention consist of one of the iron group metals; i.e., iron, cobalt, nickel and their mixtures; and a refractory metal; i.e., molybdenum, tungsten and their mixtures.

The metals are used in amounts such that of the total metal content, 5 to 90 weight percent is iron, cobalt, nickel or their mixtures, and to 95 percent is tungsten, molybdenum, or their mixtures. It has been found that these ratios of iron group metal to tungsten or molybdenum result in the beneficial effects growing out of balanced thermal coefiicients of expansion. Of the iron group metals, it is preferred to use nickel, and of molybdenum and tungsten, molybdenum is preferred.

The iron group metal and molybdenum or tungsten are preferably used in amounts of 40 to 80 weight percent of iron group metal and 20 to 60 weight percent of tungsten or molybdenum, and most preferably in amounts of 40 to 60 weight percent of iron group metal and 40 to 60 weight percent of tungsten or molybdenum. Such ratios contribute exceptional toughness to the compositions of this invention without softening the compositions unduly.

The amount of metal which should be present in the compositions of this invention ranges from 1 to 20 volume percent. At least 1 volume percent of the metal is necessary to achieve the desired toughness in the compositions of this invention and restricting the amount to 20 volume percent helps insure necessary hardness and wear resistance.

It should be understood that within the range of 1 to 20 volume percent metal, consisting of 5 to 90- weight percent iron group metal and 10 to 95 weight percent tungsten or molybdenum, there are some combinations of metal amount and metal composition which are more preferred than others. However, generally speaking it is preferred that the higher the metal content of the composition the higher the tungsten or molybdenum content of the metal.

It is very difficult to determine the form in which the metals are present in the dense compositions of this invention. For example, it is known that tungsten or molybdenum can interact with carbides such as titanium or zirconium monocarbide in such a way that some of the tungsten or molybdenum go into the carbide crystal lattice. It is also known that at high temperatures nickel will interact with aluminum oxide to form small amounts of nickel oxide-aluminum oxide spinel. However for purposes of clarity and simplicity, references hereinafter to the metal content and to iron, cobalt, nickel, tungsten and molybdenum will be understood to refer to the metallic form even though some of these may have interacted with other components. Thus the metal portion of the dense products of this invention is considered to consist of the iron, cobalt, nickel, tungsten and molybdenum present and the zirconium, hafnium and titanium present are considered to be in the form of monocarbides, with the exception that any excess carbon which is present is presumed to be combined with tungsten or molybdenum. The aluminum which is present is considered to be in the form of aluminum oxide, A1 0 The metals suitable for use in the compositions of this invention can be obtained as powders from commercial sources or can be prepared by known methods. The metal powders should have a particle size of less than 10 microns and preferably less than 2 microns.

(d) Impurities.The components to be used in the compositions of this invention are preferably quite pure. In particular it is desired to exclude impurities such as oxygen which would tend to have deleterious effects on the dense compositions of this invention.

On the other hand minor amounts of many impurities can be tolerated with no appreciable loss of properties.

Thus the metal can contain small amounts of other metals such as titanium, zirconium, tantalum or niobium as minor impurities, although low melting metals like lead should be excluded. Small amounts of carbides other than titanium, zirconium or hafnium carbide, such as several percent of tungsten carbide, which is sometimes picked up in grinding, can be present. Even oxygen can be tolerated in small amounts such as occurs when titanium carbide has been exposed to air resulting in a few percent of titanium oxy-carbide. However, after the powder components have been milled together and are in a highly reactive state, oxidation, particularly of the metals, occurs easily and should be avoided.

Structural characteristics In addition to characterizing the compositions of this invention 0n the basis of the components discussed above, the compositions can also be characterized on the basis of their structural characteristics.

(a) Continuous phase of carbide and metal.The compositions of this invention are characterized as containing fine-grained alumina distributed throughout a continuous phase of carbide and metal.

While the effects of the presence of the alumina grains and the carbide-metal continuous phase are not completely understood, it is believed that they contribute substantially to the unusual properties of the compositions of this invention, resulting in compositions much stronger and more impact-resistant than conventional titanium carbide cutting tools or alumina ceramic cutting tools.

The presence of the alumina grains distributed in the carbide-metal phase can be determined from analysis of the dense composition. The lack of a continuous network of alumina can be ascertained by removing the carbide and metal by anodic etching in 10% ammonium bifluoride solution. Such etching removes the electrically conducting material from the outer portion of the composition nearest the surface and would result in a non-conducting surface having an electrical resistivity of greater than 100,000 micro-ohm-centimeter if the alumina was present as a continuous phase.

A convenient method for removing all of the metal and carbides from the compositions of this invention and thus demonstrating the lack of an alumina skeleton is to immerse small bars of the composition in a mixture of 25 cc. of 12 percent hydrofluoric acid and 5 cc. of concentrated nitric acid. The bars are 0.070 inch by 0.070 inch by 1.00 inch in dimensions and they are left in the acid mixture for 24 hours during which the mixture is heated on a steam bath. The portion of the bar which remains after 24 hours is alumina and can be examined for lack of continuity by visual means. At about 20 volume percent alumina or more there is usually a weak, but self-supporting structure, and below 20 volume percent there is usually no continuous skeleton of alumina. Removal of electrically conducting phases from the compositions containing from up to 20 volume percent alumina usually results in the recovery of alumina powder.

The presence of a continuous phase of the electrically conducting carbide and metal is apparent from the electrical conductivity of the dense compositions of this invention. The compositions of this invention ordinarily have a specific electrical resistivity of less than about 500 microohm-centimeter and freqe-untly less than 200 micro-ohmcentimeter.

(b) Homogeneity and fine-grained structure-The compositions of this invention are also characterized as having a fine grain size, smaller than 10 microns and preferably smaller than 5 microns in average grain diameter. Moreover the grain size is uniform and homogeneous throughout the composition and there is essentially no porosity in the dense compositions of this invention. Distribution of the alumina in the continuous phase is also uniform and homogeneous, and generally speaking any area 100 microns square which is examined microscopically at 1000 magnification will appear the same as any other area 100 microns square, within conventional statistical distribution limits.

The fine grain size of the compositions of this invention may be at least partly responsible for the good resistance to heat cracking. It also contributes along with the homogeneity and low porosity to the abrasion resistance of the compositions of this invention. Metal inclusions such as the carbide inclusions in cast iron abrade even the hardest of the metal-bonded, carbide cutting tools. Nevertheless the compositions of this invention are quite abrasion resistant.

Preparation The preparation of the compositions of this invention is important, in that many of the characteristics of the compositions are achieved as a result of the manner in which they are prepared. Thus the use of fine-grained starting materials and thorough milling of the mixed components are directly related to the fine grain size and uniform homogeneity of the compositions. Other precautions observed in preparing the compositions of this invention which have important effects on the products are:

(1) the prevention of excessive contamination from grinding media and moisture or oxygen in the air;

(2) hot-pressing or sintering under conditions which permit the escape of volatile materials prior to densification;

(3) avoiding undue absorption of carbon from pressing molds by limiting their contact under absorption-promoting conditions;

(4) avoiding excessive component recrystallization and resultant segregation by avoiding prolonged subjection to very high temperatures.

(a) Milling and powder recovery.Milling of the components, to homogeneously intermix them and obtain very fine grain sizes, is carried out according to the practices common in the art. Optimum milling conditions will ordinarily involve a mill half-filled with a grinding medium such as cobalt bonded tungsten carbide balls or rods, a liquid medium such as a hydrocarbon oil, an inert atmosphere, grinding periods of from a few days to several weeks, and powder recovery also in an inert, atmosphere. The recovered powder is ordinarily dried at temperatures of around 0200 C. under vacuum, followed by screening and storage when desirable in an inert atmosphere.

(b) Consolidation.The compositions of this invention are ordinarily consolidated to dense pore-free bodies by cold-pressing and sintering or by sintering under pressure. One preferred method of consolidation is by hot-pressing the mixed powders in a graphite mold under vacuum.

When the powders are hot-pressed they are placed in the mold and inserted into the heated zone of the hot press without application of pressure thus allowing volatile impurities to escape before the composition is densified. Full pressure is usually applied at or near the maximum temperature.

Maximum temperatures range between 1400 and 1900" C. depending upon the amount of iron group metal present and will ordinarily be between 1600 and 1800 C. Maximum pressures range between 500 and 4000 p.s.i. with lower pressures being used usually in combination with lower temperatures for compositions with a high metal content, especially when the metal is rich in iron, cobalt, nickel, or their mixtures. Conversely, higher pressures and temperatures are employed for compositions low in metal and particularly when the metal is predominantly molybdenum or tungsten.

As will be apparent, at higher temperatures and pressures some of the lower melting metal components Will tend to squeeze out of the compositions during densification. This tendency can be used to advantage by starting with a little more iron group metal than is desired, and operating at a high temperature and pressure. By this procedure some of the iron group metal will be squeezed out to give the desired metal content and the molten metal that is eliminated will act as a lubricant and sintering aid during pressing. By this means voids can be eliminated in spite of the highly refractory nature of the final composition.

It is important that the composition not be heated to a temperature, or for a period of time, which is in excess of that required to eliminate porosity and achieve density. Such higher temperatures or longer times result in unde sirable grain growth and a resultant coarsening of the structure, and can even result in development of secondary porosity due to recrystallization, or the formation of un desirable phases.

As will be demonstrated hereinafter, pressing temperatures in the range of 1700 to 1900 C. are usually employed for the preferred products of this invention and maximum temperature is applied for less than 30 minutes, usually no more than 10 minutes and preferably no more than 5 minutes after which the product is removed from the hot zone. By these procedures the compositions of this invention are compacted such that porosity is eliminated and maximum density attained without undue recrystallization. Such products are characterized by their fine grain size and outstanding transverse rupture strength.

The compositions of this invention, particularly those with high metal content and small particle sizes, can also be densified by cold-pressing and sintering under high vacuum provided that the above limitation on minimum sintering time at maximum temperature is followed. -It is preferred to isostatically press the powder in a sealed rubber mold suspended in water in an isostatic press capable of applying high pressures (60,000 psi.) hydraulically.

Utility The compositions of this invention can be employed in a variety of types of cutting tools designed for numerous use applications. They can be molded or cut into standardized disposable inserts, suitable for turning, boring or milling; or, they can be laminated with or otherwise bonded to metal-bonded carbides or tool steels for regrindable types of tooling. They are suitable generally for metal removal of ferrous metals including machining or cutting hardened steels, alloy steels, maraging steels, cast iron, cast steel, nickel, nickel-chromium alloys, nickel based and cobalt superalloys, as well as for cutting nonmetallic materials such as fiberglass-plastic laminates and ceramic compositions.

The compositions of this invention are best suited for high speed milling of such metals as alloy steels, such as AISI 4340 steel. This is so because of the great resistance to heat-cracking and the good strength and toughness of the'compositions of this invention at elevated temperatures. Because of their good thermal shock resistance they are particularly well suited for making repeated short cuts or other interrupted cuts in which the temperature of the cutting edge fluctuates rapidly.

The compositions of this invention can also be used in general refractory uses such as thread guides, bearings, wear-resistant mechanical parts, and as grit in resinbonded grinding wheels and cutoff blades. In addition the compositions of this invention are useful in any application where their combination of refractory properties, electrical conductivity, metallophilic nature, and thermal shock resistance offer an advantage such as in making an electrically conducting grit for grinding wheels to be employed in electrolytic grinding.

This invention will be better understood by reference to the following illustrative examples wherein parts and percentages are by weight unless otherwise noted.

EXAMPLE 1 This is an example of a composition containing 10 volume percent ofaluminum oxide, 85 volume percent of.

titanium carbide and volume percent of metal consisting of about 53.4 percent by weight of molybdenum and about 46.6 percent by weight of nickel.

The alumina in the form of very finely divided alpha alumina is prepared from colloidal boehrnite by heating for 18 hours in air at 350 C., then increasing the heat at 100 C. per hour to a goal temperature of 1200 C., where it is held for 24 hours. A sample of the cooled product is then treated with hydrofluoric acid and is 88% insoluble in 24% aqueous hydrofluoric acid over a period of 16 hours, indicating an alpha alumina content of 88%. The specific surface area of the HF insoluble alumina is 8.6

mP/g. as measured by nitrogen adsorption using the Brunauer, Emmett, Teller method. This surface area corresponds to a crystallite size of alpha alumina of about 175 millimicrons average particle diameter. Under an electron microscope the alpha alumina appears as aggregates of alumina crystals in the range from 100 to 300 millimicrons in diameter.

The titanium carbide used has a nonimal particle size of 2 microns and a specific surface area of 3 m. g. as determined by nitrogen adsorption. An electron micrograph shows that the titanium carbide grains are approximately 2 microns in diameter and are clustered in the form of loose aggregates. The carbon content is 19.0% and the oxygen analysis indicates a titanium dioxide content of about 2.5%.

The molybdenum powder used has a grain size of less than 325 mesh and a specific surface area as determined by nitrogen adsorption of 0.29 m. g. and an average crystallite size of 354 millimicrons as determined by X-ray diffraction line-broadening. An electron micrograph shows the molybdenum powder consists of grains /2 to 3 microns in diameter clustered together in open aggregates. Chemical analysis of the powder reveals 0.2 percent oxygen and no other impurities in amounts over 500 p.p.m.

The nickel used is a fine powder containing 0.15% carbon, 0.07% oxygen, and less than 300 p.p.m. iron. The specific surface area of the nickel powder is 0.48 m. /g. and its X-ray diffraction pattern shows only nickel, which from the line broadening has a crystallite size of 150 millimicrons. Under electron microscope, the powder appears as polycrystalline grains 1 to 5 microns in diameter.

The powders are milled by loading 6000 grams of preconditioned cylindrical cobalt-bonded tungsten carbide inserts, inch long and A inch in diameter, into a 1.3 liter steel rolling mill about 6 inches in diameter, also charged with 375 mls. of Soltrol 130 saturated paraffinic hydrocarbon, approximate boiling point 130 centigrade. The mill is then charged with 11.9 grams of the alpha alumina, 125.6 grams of the titanium carbide powder, 7.65 grams of the molybdenum powder, and 6.68 grams of the nickel powder, all as above described.

The mill is then sealed and rotated at rpm. for 5 days. The mill is then opened and the contents emptied while keeping the milling inserts inside. The mill is then rinsed out with Soltrol 130 several times until all of the milled solids are removed.

The milled powder is transferred to a vacuum evaporator, and the excess hydrocarbon is decanted off after the suspended material has settled. The wet residual cake is then dried under vacuum with the application of heat until the temperature within the evaporator is between 200 and 300 C., and the pressure is less than about 0.1 millimeter of mercury. Thereafter the powder is handled entirely in the absence of air.

The dry powder is passed through a 70 mesh screen in a nitrogen atmosphere, and then stored under nitrogen in sealed plastic containers.

A consolidated billet is prepared from this powder by hot pressing the powder in a cylindrical graphite mold having a cylindrical cavity 1 inch in diameter and fitted with opposing close-fitting pistons. One piston is held in place in one end of the mold cavity while 22 grams of the powder is dropped into the cavity under nitrogen and evenly distributed by rotating the mold and tapping it lightly on the side. The upper piston is then put in place under hand pressure. The assembled mold and contents are then placed in a vacuum chamber of a vacuum hot press, the mold is held in a vertical position, and the pistons extending above and below are engaged between opposing graphite rams of the press under pressure of about to 200 p.s.i. Within a period of a minute the mold is raised into the hot zone of the furnace at 1175 C. and at once the furnace temperature is increased while the positions of the rams are locked so as to prevent further movement during the heatup period. The temperature is raised from 1175 to 1800 C. in 10 minutes, and the temperature of the mold is held at 1800 C. for another 2 minutes to ensure uniform heating of the sample. A pressure of 4000 p.s.i. is then applied through the pistons for four minutes. Immediately after pressing, the mold and contents, still being held between the opposing rams, is moved out of the furnace into a cool zone where the mold and contents are cooled to dull red heat in about 5 minutes.

The mold and contents are then removed from the vacuum furnace and the billet is removed from the mold and sand blasted to remove any adhering carbon.

Chemical analysis shows, in addition to the alumina, titanium carbide, molybdenum and nickel, the presence of about 2% of iron, presumably attrition from the mill, and 4% by weight of tungsten presumably present as tungsten carbide and about 0.5% of cobalt, both probably picked up from attrition of the milling inserts.

The billet, which is 1 inch in diameter and about 0.30 inch in thickness, is cut so that a piece slightly larger than one half inch square is removed from the center. Strips 0.070 inch in thickness are cut from the material remaining to each side of this center piece and are further cut in 0.70 inch x 0.70 inch square bars for testing transverse rupture strength. Other portions of the billet are used for indentation hardness tests and for other product characterization. The transverse rupture strength as measured by bending the 0.070 inch X 0.070 inch test bars on a y inch span is about 170,000 p.s.i. The hardness is 94.0 on the Rockwell A scale.

On inspection, the hot pressed composition is not visibly porous. Structurally the composition consists of an extreme fine-grained phase titanium carbide, nickel, and molybdenum, with alumina grains dispersed uniformly throughout the structure.

The composition has a specific resistivity of 119 microohm cm. This conductivity indicates continuity of the conducting components of the structure, namely, the metal and titanium carbide. Electron micrographs indicates a very fine grain structure, few grains exceeding 1 or 2 microns in size. The alumina is generally the coarsest phase.

The discontinuity of the alumina phase is indicated by removing the titanium carbide and metal from the composition by anodic attack for 24 hours in a warmed, mixed solution of dilute hydrofluoric acid and concentrated nitric acid. The structure disintegrates in the Warm acid solution leaving an insoluble alumina powder and demonstrating that the alumina is not present in the structure as a continuous self-supporting skeleton.

The square centerpiece is finished as a cutting tip to exact dimensions, /2 x /2 x inch and the corners are finished with a inch radius, a style known in the industry as SNG-432. This tip is employed as a cutting insert for dry, high speed turning of class 30 (170 BHN) grey cast iron at a surface speed of 1250 feet per minute and a feed rate of 0.005 inch per revolution, with a depth of cut of 0.050 inch. Under these conditions the insert shows very good resistance to flank wear.

The same insert is also employed as a cutting insert for high speed turning of AISI 1045 steel having a hardness of 183 Brinnell. The test is carried out by machining dry for minutes, at 900 surface feet per minute and 0.005 inch feed per revolution, with a 0.050 inch depth of cut. Under these conditions the insert shows very good resistance to flank wear.

The same insert is also employed for single tooth face milling of 2 inch wide bars of AISI 4340 steel having a hardness of 340 Brinnell. The milling is carried out dry, negative rake, and on center, with a 4 inch diameter head, at 1000 surface feet per minute and 0.006 inch feed per tooth, with a 0.050 inch depth of cut. Tools in this test are ordinarily run to failure by wear, cratering, heatchecking or chipping. The single tooth of this composition performs excellently in this test and shows no heat cracking.

EXAMPLE 2 This is an example of a composition containing volume percent of aluminum oxide, 55 volume percent of zirconium carbide, 10 volume percent of hafnium carbide and volume percent of metal consisting of about 90 percent by weight of tungsten and about 10 percent by weight of cobalt.

The preparation of the powder and the hot pressing are carried out according to conditions described in Example 1, except that the charge Weights to the ball mill are 17.9 grams of alumina, 111 grams of zirconium carbide, 38.1 grams of hafnium carbide, 93.25 grams of tungsten and 10.35 grams of cobalt. The zirconium and hafnium carbides are fine powders obtained from Materials for Industry (a division of Vestron Corp., Ambler, Pa.). They have a surface area of about 0.5 square meter per gram and an oxygen content of about 0.2%.

The transverse rupture strength of the hot pressed billet is 140,000 p.s.i.

A cutting tip of this composition, prepared as in Example 1, when tested under the metal cutting conditions described in Example 1, gives good resistance to flank wear in the high speed turning test on AISI 1045 steel; very good wear resistance in the high speed turning test on grey cast iron; and good performance in the face milling test on AISI 4340 steel.

EXAMPLE 3 This is an example of a composition containing 18 volume percent of aluminum oxide, 72 volume percent titanium carbide and 10 volume percent metal consisting of 53.4 weight percent of molybdenum and 46.6 weight percent nickel.

The preparation of the powder is carried out according to the conditions described in Example 1. The charge weights to the mill are 21.5 grams of alumina, 145.3 grams of titanium carbide, 15.3 grams of molybdenum, and 13.35 grams of nickel. The alumina used is Alcoa Superground Alumina XA16 which is all alpha alumina by X-ray examination, and has a specific surface area of 13 square meters per gram. Electron micrographs show particles of 200 millimicrons or less, forming much larger aggregates.

The milled powder is loaded into a sealed rubber mold and is cold pressed in water in an isostatic press by applying 60,000 p.s.i of hydraulic pressure. The cold pressed billet is removed from the mold and sintered under a vacuum of 1X10 mm. Hg for 5 minutes at 1800 C.

The transverse rupture strength of the sintered piece is 150,000 p.s.i.

A cutting tip prepared from this composition by the procedure of Example 1, when tested according to the metal cutting conditions described in Example 1, gives excellent resistance to flank wear in the high speed turning test on AISI 1045 steel; very good wear resistance in the high speed turning test on grey cast iron; and very good performance in the face milling test on AISI 4340 steel.

What is claimed is:

1. Dense compositions having an average grain size smaller than 10 microns and consisting essentially of from 60 to 89 volume percent of a carbide selected from the group consisting of zirconium carbide, hafnium carbide, titanium carbide and their mixtures; from 10 up 20 volume percent alumina; and from 1 to 20 volume percent metal; said metal consisting essentially of 5 to 90 weight percent of a metal selected from the group consisting of iron, cobalt, nickel and their mixtures and 10 to 95 weight percent of a metal selected from the group consisting of tungsten, molybdenum and their mixtures.

2. A dense composition of claim 1 in which the carbide is titanium carbide.

3. A dense composition of claim 1 in which the metal consists essentially of nickel and molybdenum.

4. A dense composition of claim 1 in which the average grain size is smaller than 5 microns.

5. A dense composition of claim 1 in which the metal consists essentially of 40 to 60 weight percent of a metal selected from the group consisting of iron, cobalt, nickel and their mixtures and 40 to 60 weight percent of a metal selected from the group consisting of tungsten, molybdenum and their mixtures.

6. A dense composition of claim 1 in which the carbide is titanium carbide and the metal consists essentially of from 40 to 60 weight percent nickel and from 40 to 60 weight percent molybdenum.

References Cited UNITED STATES PATENTS 1,981,719 11/1934 Comstock 29182.7 X 3,249,407 5/ 1966 Alexander 29182.7 3,409,416 11/1968 Yates 75205 X W FOREIGN PATENTS 821,596 10/1959 Great Britain. 841,576 7/ 1960 Great Britain.

CARL D. QUARFORTH, Primary Examiner A. J. STEINER, Assistant Examiner US. Cl. X.R. 

